In many systems employing tubes, the interior surface of the tube will, through the course of normal use, become fouled with one or more undesired coatings. Examples of such undesired coatings include: various hard tars and residuals from petroleum products in oil pipelines; mineral scale in pipes of heat exchangers; rust or other corrosion byproducts in water (and other fluid) pipes; and plaque in veins or arteries of living beings. Such coatings typically result in a reduction of the performance of the system of which the tube forms a part. For example the performance of a heat exchanger may be degraded, a loss of pressure head may occur in a pumping system, or a reduction in flow through the tube may occur in an inlet system.
A particularly troublesome problem which has recently caused much concern is that of infestation of water inlet pipes by zebra mussels. Zebra mussels are small aquatic mussels, native to portions of Europe, which have recently been found in the St. Lawrence Seaway and in the Great Lakes of North America. Zebra mussels have a high rate of reproduction and have no known natural predators in North America. The zebra mussels attach themselves to underwater surfaces and feed by filtering organic materials from the surrounding water. Accordingly, they are particularly attracted to locations such as boat bottoms and the water inlet tubes of power plants, factories and municipal water treatment plants where water flows are prevalent.
A water inlet tube, such as that providing water to one of the above-mentioned power plants, factories or municipal water treatment plants, becomes infested when one or more zebra mussels affix themselves to the interior of the tube and begin to reproduce. The number of zebra mussels quickly rises and they will coat, and eventually block, the interior of the tube substantially reducing or even stopping the water flow through the tube.
It has proven to be difficult to remove zebra mussels from the interior of tubes in an efficient manner. Often it is required to stop flow through the infested tube and to manually scrape the mussels off the interior of the tube. This is an expensive and time consuming process and may often be impractical or difficult to accomplish depending upon the diameter of and ease of access to the tube. Further, in certain circumstances, the exact location of the zebra mussel blockage is not always readily apparent. These problems are further exacerbated by the fact that it is preferable to remove the mussels from the interior of the tubes at regular intervals rather than waiting for the system performance to degrade significantly before removing the mussels. Accordingly, this results in the requirement to remove the mussels several times a year.
Alternatives other than manual scraping have been proposed including the use of power driven crawlers which move through the tube mechanically scraping the mussels away. Unfortunately, such power driven systems include many moving parts and are expensive to manufacture and maintain. Further, such crawlers generally require that the flow through the tube be stopped and thus disposal of the mussels removed from the surface of the tube becomes a problem as a pump or other removal means must be provided.